1. Field of the Invention
The present invention relates to the preparation of an organopolysiloxane containing acrylate and/or methacrylate functional groups bonded to the polysiloxane chain through a SiC linkage.
2. Description of the Prior Art
The demand for organopolysiloxanes of the foregoing type is greatly increasing because they provide faster crosslinking rates than the commercially available vinylated organopolysiloxanes. Such organopolysiloxanes containing acrylate and/or methacrylate groups are typically in the form of diorganopolysiloxane oils and may be formulated either alone or in combination with unsaturated polymers or monomers, to be subsequently crosslinked, generally by UV radiation. Thus, U.S. Pat. No. 3,577,264 describes film-forming paint binders, which can be crosslinked by radiation, containing such oils. U.S. Pat. No. 4,035,355 describes the crosslinking of these oils in an anaerobic medium. European Patent EP-A-016,663 describes their use as antiadhesive coatings. Silanes which can be hydrolyzed, useful as adhesion enhancers for fiberglass reinforcing materials, are described in British Patent No. 949,126, certain of these silanes being prepared by the hydrosilylation of allyl methacrylate.
However, it is well known from the literature that the reaction of hydrosilylating compounds containing an allyl substituent in the presence of a platinum catalyst may give rise to undesirable secondary reactions, especially those entailing production of propene, unless the silicon hydride contains electron donor groups such as chlorine or carbonyl groups. Compare in this respect J. L. Speier et al, J. AM. CHEM. SOC., 82, 3601 (1980) and U.S. Pat. Nos. 4,503,208 and 3,767,690.
U.S. Pat. Nos. 4,011,247 and 4,554,339 describe diorganopolysiloxanes containing both acryloxy units and SiH units.
According to U.S. Pat. No. 4,554,339, gammahydroxypropylated oils are esterified at the end of the polymer chain with acrylic acid utilizing an acidic earth of the montmorillonite type. This process has the disadvantage of requiring separation of the solid catalyst upon completion of the reaction.
A process for the preparation of diorganopolysiloxane oils containing acrylate and/or methacrylate groups, and which ma additionally contain hydroxyalkyl groups, by reacting the corresponding diorganopolysiloxane oil containing hydroxyalkyl groups with acryloyl or methacryloyl chloride, in the presence of triethylamine and forming the corresponding amine hydrochloride, is described in U.S. Pat. Nos. 4,261,875 and 4,294,974. The principal disadvantage of this method is precisely the need for the removal of the amine hydrochloride produced.
Moreover, the following phenomena are well known in organic chemistry, outside the field of the silicones:
(i) preparation of esters of higher alcohols, deemed heavy esters, by the transesterification of an ester of a lower alcohol, deemed a light ester, with such higher alcohols; PA1 (ii) promotion of the transesterification by using an excess of the light ester and use of such ester as the entraining agent for the lower alcohol produced during the reaction; PA1 (iii) acceleration of this reaction by using a catalyst; and PA1 (iv) optional recycling of the light ester/light alcohol fraction into the production of the light ester itself. PA1 W is a functional group which is inert towards the transesterification reaction.
This reaction, as applied to light acrylates and methacrylates and to heavy alcohols, using a titanium phenoxide (French Patent No. 2,033,441), zinc oxide (U.S. Pat. No. 3,714,234) and dialkyltin oxide (East German Patent DD-A-205,891) is known.